1. Field of the Invention
The present invention relates to an image reading apparatus used for reading images such as images printed on a document page.
2. Description of the Related Art
FIG. 12 is a sectional view illustrating an image reading apparatus B as an example of conventional image reading apparatus. The image reading apparatus B is elongated in the primary scanning direction (i.e., the direction perpendicular to the cross section shown in FIG. 12) and includes a case 91, a light source (not shown), a light guide member 92, a lens unit 93, a plurality of light receiving elements 94, a substrate 95 and a glass cover 96. The light source, the light guide member 92 and the lens unit 93 are accommodated in the case 91. The substrate 95 is fixed to the case 91, with the light receiving elements 94 carried thereon and arranged in a row extending in the primary scanning direction. The glass cover 96 is fixed to the case 91 on the side opposite to the substrate 95.
The light source is configured to emit light of a predetermined wavelength. The light guide member 92 converts the light from the light source into linear light extending in the primary scanning direction and then emits the light toward the glass cover 96, upon which an image-carrying object (not shown) is placed. The lens unit 93 converges the reflected linear light from the object onto the light receiving elements 94. Upon receiving the light, the light receiving elements 94 output a luminance signal corresponding to the amount of received light.
The image reading process by the image reading apparatus B is performed as follows. The image-carrying object is moved in the secondary scanning direction (i.e., lateral direction in FIG. 12) relative to the glass cover 96 at a constant speed, linear light is emitted from the light guide member 92 to the image-carrying object. For each line (extending in the primary scanning direction) of the surface of the image-carrying object, the light receiving elements 94 receive, via the lens unit 93, the light reflected by the image-carrying object and output a luminance signal of a level corresponding to the amount of light received. In this way, the image on the surface of the object, is read as image data. Image reading apparatuses are disclosed in e.g. JP-A-2001-223844 and JP-A-2004-266313.
Generally, paper bills and the like include an image printed with invisible ink, in addition to an image printed with visible ink. Images printed with invisible ink, which emit fluorescent light when illuminated with ultraviolet light, are useful for discriminating genuine paper bills from counterfeit paper bills. Thus, to check whether an object like a paper bill is genuine or counterfeit, it is useful to read the content printed on the object with invisible ink in addition to the content printed with visible ink. To read the content printed with visible ink by an image reading apparatus, it is necessary to illuminate the object with visible light or infrared light. To read the content printed with invisible ink by an image reading apparatus, it is necessary to illuminate the object with ultraviolet light.
Since the wavelength of visible light and that of infrared light are significantly different, the index of refraction of a light guide member with respect to visible light or infrared light is greatly different, from that with respect to ultraviolet light. Thus, when a light guide member 92 suitable for guiding visible light or infrared light is employed for the above-described image reading apparatus B, ultraviolet light cannot be directed to the image-carrying object as prosper linear light even when an ultraviolet light source for emitting light toward the light guide member is provided in the image reading apparatus in addition to a visible light source or an infrared light source. Conversely, when a light guide member 92 suitable for guiding ultraviolet light is employed for the above-described image reading apparatus B, visible light or infrared light cannot be directed to the image-carrying object as proper linear light even when a visible light source or an infrared light source for emitting light toward the light guide member is provided in the image reading apparatus in addition to an ultraviolet light source. Thus, with the conventional technique, to determine whether an object like a paper bill is genuine or counterfeit, image reading needs to be performed by using two image reading apparatuses, i.e., one including a light guide member capable of emitting visible light or infrared light as proper linear light and one including a light guide member capable of emitting ultraviolet light as proper linear light.
The present, invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide an image reading apparatus configured to perform reading processes using significantly different wavelengths of light.